Return an approved agent answer as output_type after human review

[kaxil]

With enable_hitl_review=True, AgentOperator ran the approved text through json.loads unless output_type was a Pydantic model. So with the default output_type=str, an approved answer of 42 came back as an int, and one that looked like a JSON object came back as a dict. @task.llm returns the same text unchanged.

It now uses the same conversion as LLMOperator's approval path: a str output passes through unchanged, any other output_type is validated from the JSON, and an edit the type rejects falls back to the reviewer's text. The new test fails on the old code for the two str cases.

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